Caution! The air lines for the heated oxygen sensors (HO2S) must not be trapped or damaged in any way. The connectors for the heatedoxygen sensors (HO2S) must not be greased under any circumstances. The oil in the grease would disrupt the reference air and the function ofthe heated oxygen sensors (HO2S).

The rear heated oxygen sensor (HO2S) is used to provide the Engine Control Module (ECM) with information about the remaining oxygen content of theexhaust gases behind the three-way catalytic converter (TWC). This information is used by the Engine Control Module (ECM) to check the function ofthe three-way catalytic converter (TWC). This check is carried out when the conditions for the Rear heated oxygen sensors (HO2S) are used to providethe Engine Control Module (ECM) with information about the remaining oxygen content of the exhaust gases behind the three-way catalytic converter(TWC). This information is used by the Engine Control Module (ECM) to check the function of the three-way catalytic converter (TWC). This check iscarried out when the conditions for the catalytic converter diagnostics have been met. Rear heated oxygen sensors (HO2S) have no direct effect onregulation of the fuel/air mixture. However the Engine Control Module (ECM) uses the signal to optimize the signal from front heated oxygen sensors(HO2S). For further information, see: Three-way catalytic converter (TWC) diagnostics See: Powertrain Management/Computers and ControlSystems/Description and Operation/Three-Way Catalytic Converter (TWC) Diagnostics The heated oxygen sensor (HO2S) uses voltage control. The signal characteristic is binary. With a binary signal characteristic, the amplitude of thesignal curve changes considerably when changing the oxygen content in the exhaust gases. Otherwise its components and function are the same as thefront heated oxygen sensor (HO2S).There are two rear heated oxygen sensors; one for bank 1 and one for bank 2.The heated oxygen sensors (HO2S) can be diagnosed by the engine control module (ECM), and signals from them can be read off

Preheating of the heated oxygen sensors (HO2S)

The heated oxygen sensor (HO2S) only functions above a certain temperature, approximately 300° C. The normal operating temperature is between300-900° C. The heated oxygen sensors (HO2S) are electrically pre-heated so that operating temperature is rapidly reached. They are also pre-heated toensure that the heated oxygen sensors (HO2S) maintain a normal operating temperature and to prevent condensation which could damage the heatedoxygen sensor (HO2S).The sensor's heating coil consists of a PTC-resistor. The heating coil is supplied with voltage from the system relay and is grounded internally in theEngine control module (ECM).When the control module grounds the connection, a current will pass through the PTC-resistor. When the heated oxygen sensor is cold, the resistance inthe PTC-resistor is low and a high current will pass through the circuit. To avoid condensation damage to the heated oxygen sensor the current is pulsedfrom the Engine control module (ECM) in the beginning. Depending on the temperature, consideration is given to dew point and, as the temperatureincreases in the PTC-resistor, the resistance increases in the resistor, the current is reduced and transfers gradually to non-pulsing current.The heating period for the front heated oxygen sensor is short, approx. 20 seconds.The heater element heats the heated oxygen sensors (HO2S) to approximately 350 °C. The probes maintain this as a minimum temperature.The engine control module (ECM) can diagnose the heater element.